Electronic proximity sensor which is responsive to induced resistance

Claim 2

A proximity sensor circuit comprising: (a) a transformer containing first, second, and third mutually inductively coupled windings, each having a first and second end, (b) a probe including a coil connected across said first winding, (c) a capacitor connected across said second winding, the combination forming an LC resonating circuit, (d) first and second transistors each having first, second and third elements, the first element of said first transistor being connected to the first end of said second winding, and the second element of said second transistor being connected to the first end of said third winding, (e) a source of voltages having first, second and third terminals providing three different voltage potentials, the first terminal being connected to the second end of said second winding and to the first element of said second transistor, and the second terminal being connected to the second end of said third winding and to the second element of said first transistor, (f) a resistor having a first end connected to the third elements of said transistors, and having a second end connected to the third terminal of said source of voltages.

Claim 3

The circuit of claim 1 in which said transistors are NPN type junction transistors and the first, second, and third elements of said transistors are collectors, bases, and emitters respectively.

Claim 4

The circuit of claim 1 in which said second and third windings are located on said transformer in such a manner such that a current flowing from the first to the second end of said second winding induces a current that flows from the first to the second end of said third winding.

Claim 5

The circuit of claim 1 in which the first terminal of said source of voltages has a voltage potential of about 12 volts, the second terminal of said source of voltages has a voltage potential of about 5 volts, and the third terminal of said source of voltages is ground.

Claim 6

The circuit of claim 1 in which said source of voltages additionally has a fourth terminal and the circuit additionally comprises: (g) a third and a fourth transistor, said transistors being junction transistors, each said transistor having a collector, a base, and an emitter, the collector of said third transistor being connected to the emitter of said fourth transistor, the base of said third transistor being connected to the collector of said first transistor, and the base of said fourth transistor being connected to the second terminal of said source of voltages; and (h) a second resistor having one end connected to the fourth terminal of said source of voltages, and having the other end connected to the emitter of said third transistor.

Claim 7

The circuit of claim 5 in which the fourth terminal of said source of voltages has a voltage potential of about 12 volts.

Claim 8

The circuit of claim 5 additionally comprising: (i) filter circuitry means for detecting changes in voltage which occur at a specified frequency which is a lower frequency than the frequency of oscillation of said LC circuit, said filter circuit means being connected to the collector of said fourth transistor.

Claim 9

The circuit of claim 5 additionally comprising: (j) parts present detector circuit means for sampling the voltage at the collector of said fourth transistor and for producing a signal that is in one state when a metal object is in proximity with said probe and in another state when no metal object is in proximity with said probe.

Claim 10

The circuit of claim 5 additionally comprising: (k) probe fault detector circuit means for sampling the voltage at the collector of said fourth transistor and for producing a signal that is in one state when there is an electrical short in said probe and when there is an electrical open condition in said probe and is in another state at all other times.

Claim 11

A circuit responsive to induced resistance comprising: (a) a probe having a coil, and (b) a sensor circuit coupled to said probe, said sensor circuit having an LC resonating circuit and having an output signal that is primarily responsive to the induced resistance into said LC resonating circuit through said probe as opposed to induced reactance through said probe; (c) a parts present detector means for receiving the output signal from said sensor circuit and for producing a signal that is responsive to induced resistance indicative of the existence of a conductive object in proximity with said probe; and (d) probe fault circuit means for receiving the output signal from said sensor circuit means and for producing a signal responsive to about zero induced resistance indicative of an electrical short circuit in said probe and is responsive to about indefinite induced resistance indicative of an electrical open condition in said probe, said probe fault detector circuit including: a transistor having a collector, a base, and an emitter, a first resistor connected to the base of said transistor, a source of voltages having first and second terminals providing two different voltage potentials, a second resistor having higher resistance than said first resistor; and having one end connected to the collector of said transistor and the other end connected to the first terminal of said source of voltages, a third resistor having about the same resistance as said second resistor; and having one end connected to the emitter of said transistor and the other end connected to the second terminal of said source of voltages, a comparator having an input voltage point, a reference voltage, and an output voltage, and a fourth resistor having higher resistance than said second and said third resistors; and having one end connected to the input voltage point of said comparator and other end connected to the second terminal of said source of voltages.

Claim 12

A circuit responsive to induced resistance comprising: (a) a probe having a coil, and (b) a sensor circuit coupled to said probe, said sensor circuit having an LC resonating circuit and having an output signal that is primarily responsive to the induced resistance into said LC resonating circuit through said probe as opposed to induced reactance through said probe; (c) a parts present detector means for receiving the output signal from said sensor circuit and for producing a signal that is responsive to induced resistance indicative of the existence of a conductive object in proximity with said probe; and (d) probe fault circuit means for receiving the output signal from said sensor circuit means and for producing a signal responsive to about zero induced resistance indicative of an electrical short circuit in said probe and is responsive to about indefinite induced resistance indicative of an electrical open condition in said probe, said probe fault detector circuit including: a transistor having a collector, a base, and an emitter, a first resistor connected to the base of said transistor, a source of voltages having first and second terminals providing two different voltage potentials, a second resistor having higher resistance than said first resistor; and having one end connected to the collector of said transistor and the other end connected to the first terminal of said source of voltages, a third resistor having about the same resistance as said second resistor; and having one end connected to the emitter of said transistor and the other end connected to the second terminal of said source of voltages, a comparator having an input voltage point, a reference voltage, and an output voltage, and a fourth resistor having higher resistance than said second and said third resistors; and having one end connected to the input voltage point of said comparator and other end connected to the second terminal of said source of voltages.

Claim 13

A circuit responsive to induced resistance comprising: (a) a probe having a coil, and (b) a sensor circuit coupled to said probe, said sensor circuit having an LC resonating circuit and having an output signal that is primarily responsive to the induced resistance into said LC resonating circuit through said probe as opposed to induced reactance through said probe; (c) a parts present detector means for receiving the output signal from said sensor circuit and for producing a signal that is responsive to induced resistance indicative of the existence of a conductive object in proximity with said probe; and (d) probe fault circuit means for receiving the output signal from said sensor circuit means and for producing a signal responsive to about zero induced resistance indicative of an electrical short circuit in said probe and is responsive to about indefinite induced resistance indicative of an electrical open condition in said probe, said parts present detector circuit including: a transistor having a collector, a base, and an emitter, a first resistor connected to the base of said transistor, a source of voltages having first and second terminals providing two different voltage potentials, a second resistor having higher resistance than said first resistor and having one end connected to the collector of said transistor and the other end connected to the first terminal of said source of voltages, a third resistor having about the same resistance as said second resistor; and having one end connected to the emitter of said transistor and the other end connected to the second terminal of said source of voltages, a comparator having an input voltage point, a reference voltage, and an output voltage, and a fourth resistor having higher resistance than said second and said third resistors; and having one end connected to the input voltage point of said comparator and other end connected to the first terminal of said source of voltages.

Claim 14

A circuit responsive to induced resistance comprising: (a) a probe having a coil, and (b) a sensor circuit coupled to said probe, said sensor circuit having an LC resonating circuit and having an output signal that is primarily responsive to the induced resistance into said LC resonating circuit through said probe as opposed to induced reactance through said probe; (c) a parts present detector means for receiving the output signal from said sensor circuit and for producing a signal that is responsive to induced resistance indicative of the existence of a conductive object in proximity with said probe; and (d) probe fault circuit means for receiving the output signal from said sensor circuit means and for producing a signal responsive to about zero induced resistance indicative of an electrical short circuit in said probe and is responsive to about indefinite induced resistance indicative of an electrical open condition in said probe, said parts present detector circuit including: a transistor having a collector, a base, and an emitter, a first resistor connected to the base of said transistor, a source of voltages having first and second terminals providing two different voltage potentials, a second resistor having higher resistance than said first resistor and having one end connected to the collector of said transistor and the other end connected to the first terminal of said source of voltages, a third resistor having about the same resistance as said second resistor; and having one end connected to the emitter of said transistor and the other end connected to the second terminal of said source of voltages, a comparator having an input voltage point, a reference voltage, and an output voltage, and a fourth resistor having higher resistance than said second and said third resistors; and having one end connected to the input voltage point of said comparator and other end connected to the first terminal of said source of voltages.

Claim 15

The circuit of claim 11 in which said probe fault detector circuit includes: (a) a transistor having a collector, a base, and an emitter, (b) a first resistor connected to the base of said transistor, (c) a source of voltages having first and second terminals providing two different voltage potentials, (d) a second resistor having higher resistance than said first resistor; and having one end connected to the collector of said transistor and the other end connected to the first terminal of said source of voltages, (e) a third resistor having about the same resistance as said second resistor; and having one end connected to the emitter of said transistor and the other end connected to the second terminal of said source of voltages, (f) a comparator having an input voltage point, a reference voltage, and an output voltage, (g) a fourth resistor having higher resistance than said second and said third resistors; and having one end connected to the input voltage point of said comparator and the other end connected to the second terminal of said source of voltages.

Claim 16

The circuit of claim 12 in which the transistor of said parts present detector circuit is also the transistor of said probe fault detector circuit.

Claim 17

The circuit of claim 13 in which the first resistor, the second resistor, the third resistor and the source of voltages of said parts present detector circuit are also the first resistor, the second resistor, the third resistor and the source of voltages of said probe fault detector circuit.

Claim 18

The circuit of claim 14 in which the transistor of said parts present detector circuit and of said probe fault detector circuit is an NPN junction transistor.

Claim 19

The circuit of claim 15 in which the first terminal of the source of voltages of said parts present detector circuit and of said probe fault detector circuit has a voltage potential of about 5 volts and the second terminal of the source of voltages of said parts present detector circuit and of said probe fault detector circuit is electrical ground.

Claim 20

The circuit of claim 16 in which said specified frequency is about 60 Hz.